Leadless pacemakers are used to sense electrical activity and/or deliver therapeutic signals to the heart. For some patients, one atrial pacemaker may be used in one atrium of the heart. In other patients, multiple leadless pacemakers may be used in at least one atrium and at least one ventricle of the heart. Each leadless pacemaker device typically includes one or more electrodes on its outer housing to deliver therapeutic electrical signals and/or sense intrinsic depolarizations of the heart. Each leadless pacemaker may be positioned within a chamber of the heart and, in some examples, may be anchored to a wall of the heart via a fixation mechanism.
In some cases, a leadless pacemaker may need to sense depolarizations of one or more chambers of the heart other than the chamber in which it is implanted, in order to time pacing signals. In dual-chamber, leadless pacemaker systems, two or more pacemakers in two or more chambers of the heart must be able to pace the chambers in synchronous fashion. At the same time, sending timing signals from one leadless pacemaker in one chamber of the heart to another leadless pacemaker in another chamber of the heart, as well as receiving and processing the delivered signals with the receiving pacemaker(s), consumes large amounts of battery power, thus decreasing the useful life of the leadless pacemaker devices.
One depolarization signal that might be sensed by an atrial leadless pacemaker device is a far-field R-wave (“FFRW”), which indicates ventricular depolarization. It is challenging, however, for currently available atrial leadless pacemakers to sense FFRWs. One reason for this difficulty is that atrial leadless pacemakers are not configured to distinguish between atrial depolarization waveforms (P-waves) and FFRWs. Additionally, FFRWs are typically undersensed by the leadless atrial pacemakers, which are designed primarily to sense P-waves. Furthermore, detection of FFRWs from an atrial leadless pacemaker is more difficult than doing so with a standard dual-chamber pacemaker, because the atrial leadless pacemaker does not know the timing of true ventricular senses and paces.
Therefore, it would be desirable to have a pacemaker device that could effectively sense depolarizations of heart chambers other than the one in which it is implanted. More specifically, it would be advantageous to have a leadless, atrial pacemaker device that could sense FFRWs and distinguish them from P-waves. Such a leadless, atrial pacemaker could use this sensed information to time pacing pulses, without requiring signaling between leadless pacemakers in multiple chambers of the heart.